Janet D. Stemwedel (whose nom de blog is Dr. Free-Ride) is an associate professor of philosophy at San Jose State University. Before becoming a philosopher, she earned a Ph.D. in physical chemistry. Email her at dr.freeride@gmail.com.
Dr. Free-Ride: So, you know this Friday is Mole Day.
Elder offspring: It is? What does that mean exactly?
Dr. Free-Ride: Do you remember what a mole is? Not the animal, but the quantity.
Elder offspring: Not really.
Dr. Free-Ride's better half: It's a convenient unit of measure for things like atoms and molecules.
Dr. Free-Ride: Like eggs come in dozens and shoes come in pairs, molecules come in moles -- that's 6.02 x 1023.
Elder offspring: Whoa! That's a pretty big number.
Dr. Free-Ride's better half:Well, but atoms and molecules are pretty small. Can you imagine weighing out a single carbon atom?
Elder offspring: No.
Dr. Free-Ride's better half: But can you imagine weighing out 12 grams of carbon?
Elder offspring: Sure!
Dr. Free-Ride's better half: And do you know how many carbon atoms there are in 12 grams of carbon?
Dr. Free-Ride: 6.02 x 1023!
Elder offspring: A mole.
Dr. Free-Ride's better half: Yep. And if you weigh out 58.5 grams of sodium chloride?
Elder offspring: You mean salt? Is that a mole of salt?
Dr. Free-Ride: 6.02 x 1023 molecules!
Dr. Free-Ride's better half: You know, the ending "cule" on the word "molecule" means something like "little". Like an "animalcule" is a little animal.
Dr. Free-Ride: A microscopic one.
Elder offspring: So a molecule is a little mole?
Dr. Free-Ride's better half: Uh huh. Chemists figured out that fixed proportions of the chemicals they weighed out would react with each other, so the little units of chemicals that did the reacting were called the molecules.
Elder offspring: But why call that big number --
Dr. Free-Ride: 6.02 x 1023!
Elder offspring: -- a mole?
Dr. Free-Ride's better half: That's the question, isn't it?
Physical Science
Education
